FiveThirtyEight

The College Football Playoff has transformed the way teams and conferences build their schedules — and created plenty of controversy along the way — in the four seasons since it debuted. And even if the system could stand to make some improvements, it’s also been a relatively successful experiment in adding legitimacy to a championship that used to be determined through such opaque measures as media voting and computer ratings. For all the debate over “who’s in,” at least the eventual champion can say it won the title by beating two top-ranked opponents on the field.

The benefits of a four-team bracket got us thinking: What if the current playoff structure had been in place before 2014? Who would likely have won the championship each year? (Would it have been different from the consensus champs of old?) And which schools would have gained — and lost — the most titles under a playoff system?

Let’s answer those questions. (If you’re not interested in how we’re answering those questions, skip down to the first table.)

First, we’ll need a way to determine which teams would have made the playoff each year. Unfortunately, over the first four years of the actual playoff’s existence, neither the AP poll nor our Elo ratings (which are designed, in part, to predict the playoff selection committee’s tendencies) have completely nailed the playoff field with their four highest-ranked teams going into the bowls. But a combination of both has been a perfect 16 for 16 in terms of predicting the real-life playoff teams.

So we’ll use that Elo/AP combo to pick the four playoff teams in each historical season. (Our Elo ratings can be calculated going back to the 1988 season, so that’s when our hypothetical exercise will begin.) I also found that, once the playoff field is set, the pre-bowl AP rankings alone have done the best job of matching the committee’s seeding for the teams, so we’ll set the seeds that way in our mythical playoffs.

Next, we’ll need a way to play out the theoretical playoff games themselves. For that, we’ll use Elo, which provides a probabilistic forecast for any given game based on the two teams’ pregame ratings. In most cases, we’ll use each team’s pre-bowl Elo ratings to give us the chances of each team winning both its semifinal game and the championship game (conditional on making it that far). The only exception is when a slated matchup happened in a real-life bowl that season, in which case we’ll use the actual result for that semifinal or final matchup.

A great example of this came in 2003, when both of our hypothetical semifinal games — No. 1 USC vs. No. 4 Michigan and No. 2 LSU vs. No. 3 Oklahoma — actually played out in the Rose Bowl and Sugar Bowl, respectively. In that case, the Trojans and Tigers would automatically advance to the title game, where each would have almost exactly a 50-50 shot at winning the championship, according to Elo. At least one of these real-world matchups happened every year from 1988 to 2013 — except in 1989, when conference bowl tie-ins kept each of the four teams in our playoff field from actually playing one another.

After following all of the rules laid out above, here’s how each season since 1988 would look if a playoff had been in place instead of the system that was used at the time:

What 26 extra years of playoffs would have looked like

Hypothetical College Football Playoff fields for the 1988-2013 seasons based on Elo ratings and AP poll rankings

Actual champions (or co-champs) are listed in bold. In 1990, Georgia Tech was co-champion but is not projected to have made the playoff that season.

Playoff selection is based on pre-bowl Elo ratings and AP polls. Playoff games are simulated using Elo, except in cases where a matchup actually took place during bowl season (in which case the actual result was used). Certain teams are listed with a 0 percent championship probability because they lost a real-life game against a fellow playoff team.

Source: Sports-Reference.com

The good news for the old system(s) is that each year’s real-world national champ — or at least the co-champ — would be the favorite to win the playoff as well. (The only time a historical national champ didn’t make our theoretical playoff was in 1990, when Georgia Tech claimed the national title in the coaches’ poll but missed the top four in our rankings after entering the bowls seventh in Elo.) But the fact that the real-world champ tended to be the favorite in our hypothetical playoffs is no guarantee those seasons would have played out the same way: Even after including real bowl results when they happened, the championship favorite in any given year had only a 47 percent chance of winning the title on average.

The most uncertain year of our hypothetical playoffs might have been the aforementioned 1989 campaign; without any real-life bowls to help guide us, our system gives all four teams at least a 20 percent chance of winning the national championship. And among years that featured at least one actual bowl result to work with, the wacky 2007 season — in which playoff favorite LSU would have only a 33 percent of replicating its real-world championship — probably would have kept providing us thrills well into January. But with a playoff in place, many seasons would likely have had different endings than the ones we’ve set to memory over the years.

How different? Here are all the schools that would have made at least one playoff appearance under our hypothetical system, along with their projected and actual national championships won:

How a playoff would have changed college football history

Most FBS college football championships by school under a hypothetical four-team playoff system, 1988-2013

Playoff selection is based on pre-bowl Elo ratings and AP polls. Playoff games are simulated using Elo, except in cases where a matchup actually took place during bowl season (in which case the actual result was used).

In 1990, Georgia Tech was co-champion but is not projected to have made the playoff that season.

Source: Sports-Reference.com

Aside from Alabama, which won the most real-life championships (four) of the 1988-2013 era but would project to have about 1.4 fewer under a playoff system, every other school’s projected title tally is within about a half-championship of its actual count, playoff or not. The anti-Bama might be Oregon, who made only one BCS title game in the years we’re covering (losing to Cam Newton and Auburn in the culmination of the 2010 season) but would figure to make three playoff bids under our hypothetical system — and probably would have given Miami more of a fight than Nebraska did in 2001. All told, the Ducks would figure to have won 0.6 more championships with a playoff than under the actual system.

Over about 25 years, a handful of national titles is about the best you can do (see Bama’s four). So even a half-championship gain is a lot. And the more marginal differences further down the list matter, too. Imagine the effect on the fan bases at Oklahoma State, Cincinnati or Northwestern (!!!) if their teams had managed to get hot during the playoff and take home the championship. In general, you can see a pattern emerge in the table above: Under a four-team playoff, the long-term effect is to take titles away from many of the top programs and give extra chances to the next tier of teams. As counterintuitive as that sounds, given the way a program like Alabama has dominated the CFP since its inception, the addition of an extra semifinal game introduces more randomness to the system, which helps teams down the list.

I once wrote that the BCS wasn’t any worse at picking champs than the College Football Playoff would be, and in a certain sense, that’s not wrong. (Again, the real-life champs each season above would have also been the favorites to win the playoff.) But the more we’ve seen teams get a chance to prove their championship merit on the field against top competition, the more appealing it is. Now I only wish college football had the current system in place for the past quarter-century instead of the confusing mismash of arrangements that preceded it.